1. Field of the Invention
This invention relates to a loudspeaker device. More particularly, the present invention relates to "coiled" exponential bass midrange horn loudspeakers which are capable of reproducing a wider range of audio frequencies than prior art folded horns without the phase distortion associated with such horns, in a cabinet that is comparable in size and shape to any conventional direct radiator loudspeaker utilizing a driving unit or driver of similar size.
Low frequency sound waves or bass sounds can be reproduced by a variety of methods; however, only the exponential horn is capable of reproducing bass frequencies with "live" quality. That is to say, only an exponential horn is able to reproduce bass waves with sufficient acoustical power, life-like transient response and without the harmonic distortion normally associated with direct radiator loudspeakers.
In a direct radiator loudspeaker system, bass frequencies are generally reproduced by the movement of a diaphragm mounted within a cabinet or enclosure, with the working side of the diaphragm exposed to the atmosphere. In order for the system to reproduce bass frequencies at an acceptable sound pressure level, the diaphragm or cone must move large volumes of air. In accomplishing this objective, the diaphragm must traverse great distances in a short period of time, but in so doing, induces a great amount of harmonic distortion. The higher the level at which the system is operated, the greater the harmonic distortion realized, and with this distortion comes a significant loss of transient response, the resultant sound waves being of high pressure and low velocity. In contrast, a horn reproduces sound waves with high velocity and very low diaphragm motion, resulting in a high level of transient response and substantial elimination of harmonic distortion. These characteristics afford the system the ability to reproduce sound waves with exacting emulation of the original sound.
2. Description of the Prior Art
Many bass horn loudspeakers are known in the prior art and among the most common are the "folded" variety, some of which are limited to location in the corner of a room for proper operation at bass frequencies. An example of a folded corner horn design is provided in U.S. Pat. No. 2,373,692, dated Apr. 17, 1945, to P. W. Klipsch. Although the acoustical performance of this type of folded horn is superior to a direct radiator-type bass loudspeaker, it lacks a great deal in the ability to effectively reproduce frequencies in the mid-range (approximately 400 to 2,600 Hz.). This problem is a direct result of folding, as the width of the horn at the folds determines the upper limit of the high frequency performance and the sound waves will not traverse a bend if the width of the bend is a half wavelength or more. The folding problem is further complicated by the fact that the horn taper is negative, wherein the flare rate is greater at the throat than at the mouth. Furthermore, the "folding" of a bass horn reduces the overall operational efficiency, as the exponential expansion rate cannot be maintained in the folds or transitions. Most folded bass horns will not effectively reproduce sound above about 500 Hz., thereby necessitating the use of a low upper limit cross-over point to a large mid-range horn.
In a complete folded bass horn loudspeaker system, the midrange horn must be rather large, in order to reproduce sound as low as the upper limit cutoff frequency of the bass horn, or driver. This combination results in a high level of acoustical phase distortion induced upon the electrical audio signal applied to the loudspeaker system, due to physical placement of the horns some distance apart. The problem is further complicated in this type of system by the fact that the larger mid-range horns cannot reproduce the highest frequencies, thus necessitating the use of a third horn and thereby inducing further distortion of the applied audio signal phase. The original audio signal is split electrically and is coupled to each respective speaker horn, resulting in not one, but three sources of sound being projected into the listening area in three different planes. The resultant sound waves from each group of frequencies arrive at the listener's ear out of phase with each other. An example of severe acoustical phase distortion in a folded-type bass horn system is found in U.S. Pat. No. 2,871,972, filed Mar. 12, 1958, to C. Q. Glassey, wherein a single driver is used for driving two horn sections, one from the working side of the driver and the other from the non-working side, resulting in one horn being 180 degrees out of phase with the other.
Another problem with prior art folded bass horn systems is the large size and weight of such units, as compared to conventional direct radiator loudspeaker systems. Although it is accepted that folded bass horn systems are far superior regarding the fidelity of the sound reproduced, when compared with direct radiator loudspeakers, especially in the bass frequency range, they still remain large and costly, which probably accounts for the fact that folded bass horns are the least common of all types of loudspeakers.
A still further problem concerning the size of prior art folded-type bass horns is the fact that due to the large size and structure of these devices, their use as a sound-reproducing unit within a small device such as a portable audio player or television receiver, is not possible. Given the state of the art of modern sound-reproducing equipment such as the digital compact disc player and the digital amplifier, the use of direct radiator loudspeakers as an alternative in connection with such equipment would not be advantageous, as it would circumvent what is gained in the advanced audio technology, by acoustically distorting the audio signal.
Other loudspeaker systems which utilize a folded or baffled configuration include U.S. Pat. No. Des. 75,617, dated June 26, 1928, to H. L. Faison. The Faison loudspeaker includes a folded horn-type speaker of ornamental design. U.S. Pat. No. 2,058,132, dated Oct. 20, 1936, to F. Cirelli, details a "Sound Box for Amplifying Horns with Loudspeakers". The device includes a sound appliance having a sound box, two amplifying horns connected to the sound box and a loudspeaker provided within the midportion of the sound box. Two slender abutting conical portions are provided in the sound box, each of which tapers convergently away from the abutment of the portions at a tapering angle which is less than 45 degrees with respect to the axis of the tapered portion in each of the portions, respectively, the horns being connected to the sound box at the smaller convergent ends thereof. A "Horn for a Loudspeaker" is detailed in U.S. Pat. No. 2,310,243, dated Feb. 9, 1943, to P. W. Klipsch. The horn detailed in this patent includes a multi-baffled loudspeaker designed for mounting in the corner of a room and provided with multiple compartments created by the internal baffles.
U.S. Pat. No. 2,731,101, dated Jan. 17, 1956, also to P. W. Klipsch, details another "Loud Speaker". The loudspeaker detailed in this patent is designed such that the entire horn is formed outside of a housing and the housing itself is characterized by a simple acoustic low pass filter. The housing forms a simple cavity which is unobstructed except for immersion of the driver unit therein. An acoustic inertance, in the form of an orifice or slit suitably formed in the housing, coacts with the cavity to provide the lowpass filter. The front panel of the housing has an opening therein and the driver unit is mounted in the cavity upon the front panel rearwardly of this opening, through which the treble sound radiation leaves the housing. The side panels of the housing extend convergingly rearwardly of the front panel to form, in conjunction with the external proximate surfaces, the horn portions of the speaker. A "Horn for a Loudspeaker" is detailed in U.S. Pat. No. 2,871,972, dated Feb. 3, 1959, to C. Q. Glassey. The Glassey horn includes a hollow housing having an aperture for establishing communication between the interior of the housing and the atmosphere; at least one vibrating diaphragm-type loudspeaker arranged within the housing; a chamber located within the housing and enclosing the speaker and having a first opening for establishment of communication between the rear side of the speaker diaphragm and the interior of the housing; and a second opening for establishing communication between the front side of the speaker diaphragm and the interior of the housing. Further included is a partition arranged within the housing for dividing the aperture into two continguous sections; a first horn substantially encircling the chamber and provided with a flare increasing in at least one dimension from the first opening to the aperture for directing the lower frequencies of the speaker from the first opening to one of the horn mouths; and a second horn having a flare increasing in at least the same dimension as the first horn from the second opening to the aperture, for directing the higher frequency of the speaker from the second opening to the other of the horn mouths, a portion of the first horn being arranged about the second horn with the partition forming a portion common to each of the horns. U.S. Pat. No. 2,801,703, dated Aug. 6, 1957, to D. W. Martin, details a "Diffused-Tone Cabinet for Organs". The device includes a rectangular cabinet having front, rear and end walls; a top and a bottom; a first horn for low frequency sound production occupying a major portion of the enclosure volume of the cabinet and having its front and rear walls defined by the front and rear walls of the cabinet, with the mouth of the first horn opening upwardly at the top of the cabinet, the top being acoustically transparent; and a second horn for high frequency sound production mounted within the cabinet and contained primarily within the body of the first horn, the second horn including a flat horn extending lengthwise of the cabinet and having an elongated slot-like mouth opening upwardly at the top of the cabinet. U.S. Pat. No. 3,944,757, dated Mar. 16, 1976, to Tsukamoto, details a "High Fidelity Moving Coil Loudspeaker". The loudspeaker includes a tubular member having a length longer than the wavelength of any one of the frequencies in a desired frequency range and having a constant cross-sectional area along its entire length. Tubular members are coupled at one end with one side of a vibrating plate or diaphragm through an acoustical transformer constituted by a cavity formed therebetween, wherein the loudspeaker is capable of reproducing sounds with high fidelity, particularly in extremely low frequency ranges. A "Folded Horn Loudspeaker System" is detailed in U.S. Pat. No. 4,313,032, dated Jan. 26, 1982, to Donald W. Thomas, et al. The system includes a rigid enclosure and an integral, exponentially curved horn projecting outwardly from the enclosure toward the listening area. A transducer housed within a sealed chamber interiorly of the enclosure communicates through an aperture into a waveguide system of substantially rectangular dimensions. A baffle-plate system deflects sound energy from the waveguide into the throat of the horn. The baffle-plate system is positioned to avoid the reflection of sound waves back into the waveguide, to thereby minimize distortion. U.S. Pat. No. 4,549,631, dated Oct. 29, 1985, to Amar G. Bose, details a "Multiple Porting Loudspeaker System". The loudspeaker system includes an enclosure of rectangular cross-section, with a baffle dividing the interior into first and second subchambers. Each subchamber is provided with a port tube for coupling the subchamber to the region outside of the enclosure. The dividing baffle carries a woofer.
This invention solves problems associated with prior art folded-type bass horn loudspeaker systems, by providing a "coiled" or convoluted bass and bass/midrange exponential horn loudspeaker system which demonstrates a significantly increased midrange sound output over prior art folded bass horns. The system may also utilize an additional small, high frequency horn oriented in such a manner that the disperson angles of both horns overlap, thereby minimizing acoustical phase distortion in a complete loudspeaker system. The system can be provided in a size and shape which is comparable with common direct radiator loudspeaker systems utilizing a driving unit of similar size.
Accordingly, it is an object of this invention to provide coiled exponential bass horn loudspeakers which exhibit significant midrange sound output, thereby eliminating the necessity for utilizing a large midrange speaker or horn in a complete system.
Another object of this invention is to provide coiled exponential bass and bass/midrange loudspeakers which utilize a miniaturized bass horn or driver in combination with a coiled horn section which is exponentially expanded and carefully convoluted so as not to disturb the cross-sectional configuration.
Yet another object of the invention is to provide coiled exponential bass/midrange horn loudspeakers which, when used in combination with a high frequency speaker or horn of small size placed at the horn mouth, results in a complete loudspeaker system exhibiting a significantly reduced level of acoustical phase distortion.
It is a further object of the invention to provide coiled exponential bass/midrange horn loudspeaker systems of varying dimension, which may employ driving units of any selected size and which are superior in sound quality to conventional loudspeakers.
A still further object of the invention is to provide a coiled exponential bass/midrange horn loudspeaker system, in which the low frequency driving unit and the high frequency horn sections are separated by a selected distance and are connected by an exponentially expanding section or path of varying length and shape, to facilitate placement within another device for reproducing sound within the cabinet of the device.
Yet another object of the invention is to provide a coiled exponential bass/midrange horn located within the cabinet of a selected device for reproducing sound, in which, to facilitate placement within the device, the driver section may be located at some distance from, but connected to the horn mouth by an exponentially expanding section or interconnected sections of varying size and length, which are coiled or tortuously laid out within the cabinet.
Another object of this invention is to provide coiled exponential bass and bass/midrange loudspeaker systems in multiple arrangements, such as side-by-side, back-to-back, bottom-to-bottom, or in other combinations, for use in theaters, auditoriums and the like, for the purpose of increasing the sound pressure level which may be required for servicing such large areas.